Climatology of Tropical Cyclones Approaching Tanzania and Their Impacts on Rainfall in East Africa

ABSTRACT

East Africa is at risk of natural disasters caused by tropical cyclones (TCs) originating over the South‐West Indian Ocean (SWIO). Generally, TCs in the SWIO move westward or southwestward and often approach or make landfall over Madagascar and Mozambique, and previous studies have therefore tended to focus on these regions. However, the impact of TCs on Tanzania has received limited attention. Here, we investigated the TC‐related impacts on Tanzania in terms of rainfall variability associated with 29 TCs that approached Tanzania (Approaching TCs), the conditions favouring TC approach to Tanzania from the open SWIO, and the factors inhibiting TC genesis over the northern seas of Madagascar (NSM) during the period 1981–2024. The Approaching TCs brought substantially enhanced rainfall (+75% to +328%) over northern Mozambique, Tanzania, and south‐central Kenya relative to the mean precipitation during the rainy season. We revealed that the likelihood of TCs approaching Tanzania is low, but such Approaching TCs can produce heavy rainfall, potentially leading to flooding. The meteorological characteristics of TCs approaching Tanzania from the open SWIO include easterly steering winds extending south of the TCs, and equatorward shift of the Mascarene High to around 20° S. For TC genesis over the NSM, 850‐hPa absolute vorticity and the 500‐hPa meridional gradient of zonal winds play important roles. These factors are associated with the seasonal variability of the Mascarene High, including its equatorward extension and westward shift, which enhance low‐level easterly wind anomalies over the low‐latitude SWIO and modulate the dynamical environment for TC genesis over the NSM. These results provide useful insight for improving the understanding of TCs that affect Tanzania, and could potentially inform future efforts toward early warning or risk reduction of regional TC‐related disasters.